报告题目：Realizing finite-momentum pairing superfluidity via a dark-state control of Feshbach resonances

报 告 人：何联毅 助理教授（清华大学物理系）

报告时间：2017年6月15日（星期四） 下午4:30

报告地点：理论物理所报告厅

Abstract: We propose that the long-sought Fulde-Ferrell superfluidity with nonzero momentum pairing can be realized in ultracold two-component Fermi gases of K-40 or Li-6 atoms, by optically tuning their magnetic Feshbach resonances via the creation of a closed-channel dark state with a Doppler-shifted Stark effect. In this scheme, two counter-propagating optical fields are applied to couple two molecular states in the closed channel to an excited molecular state, leading to a significant violation of Galilean invariance in the dark-state regime and hence to the possibility of Fulde-Ferrell superfluidity. We develop a field theoretical formulation for both two-body and many-body problems and predict that the Fulde-Ferrell state has remarkable properties, such as anisotropic single-particle dispersion relation, suppressed superfluid density at zero temperature, anisotropic sound velocity and rotonic collective mode. The latter two features can be experimentally probed using Bragg spectroscopy, providing a smoking gun proof of Fulde-Ferrell superfluidity.